Internal Revenue Service agents already try to catch tax cheats and moonshiners. Under the proposed health care legislation, they would get another assignment: checking to see whether Americans have health insurance.

The legislation would require most Americans to have health insurance and to prove it on their federal tax returns. Those who don’t would pay a penalty to the IRS.

That’s one of several key duties the IRS would assume under the bills that have been approved by the House of Representatives and Senate and will be merged by negotiators from both chambers.

The agency also would distribute as much as $140 billion a year in new government subsidies to help small employers and as many as 19 million lower-income people buy coverage.